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"The Kepler data set is unique, as it is the only one containing a population of these near Earth-analogs – planets with roughly the same size and orbit as Earth," Kepler program scientist Mario Perez said in a release. "Understanding their frequency in the galaxy will help inform the design of future NASA missions to directly image another Earth."

Kepler has now identified 4,034 planet candidates, with 2,335 verified as exoplanets. That group includes nearly 50 near-Earth size planets in the habitable zone, with 30 verified.

“This carefully-measured catalog is the foundation for directly answering one of astronomy’s most compelling questions – how many planets like our Earth are in the galaxy?” said Susan Thompson, lead author of the catalog study.

In February, NASA's Spitzer Space Telescope revealed the TRAPPIST-1 system, which features seven Earth-size planets orbiting a single star – three are in the habitable zone.